In all vehicles there is a specific oscillation behaviour of the drive train when starting, or also during driving if the drive train is excited suddenly. In vehicles having an electric motor as the drive motor, this oscillation is strongly pronounced, in particular, during starting. The reason for this is that the entire drive train can be understood in simplified terms as a spring-mass system, or as a rod spring which is inclined to oscillate as a result of corresponding excitation. In a vehicle having an electric motor drive, irregularities in the torque of the drive can arise, in particular, as a result of the mechanical design of the electric motor, of the rotational speed sensor and also a result of closed-loop control effects and activation effects in the inverter. This interference is dependent on the rotational speed and also on the load, meaning that a very broad interference spectrum can develop. As a result, at certain rotational speeds, natural frequencies can be excited by the downstream mechanical system, in particular the drive train, and resonance or resonances can occur. This oscillation of the drive train is particularly pronounced, in particular, in the lesser velocity range and when starting on an uphill gradient.
Conventional approaches to a solution for preventing said drive train oscillations or juddering are based on mechanical damping, in particular on oscillation damping by decoupling via a clutch. When an internal combustion engine is used, this oscillation can be counteracted by active adjustment of the ignition angle. A further approach to a solution which can be used in electric drives is based on strong limitation of the gradients during the build-up of torque and an associated lesser excitation of the spring system but also relatively poor dynamics of the vehicle.
German Patent Publication No. DE 10 2013 112 419 A1 discloses, for example, a method for anti-judder control of a hybrid vehicle without a torque converter, comprising: determining whether a gear shift command is output by a transmission control device of the hybrid vehicle; confirming a gear shift range which is divided into at least three phases and corresponds to the gear shift command if it is determined that the gear shift command is output; determining whether the corresponding divided gear shift range is an anti-judder-approval gear shift range; and phase reversal control of a drive motor of the hybrid vehicle by a predetermined value in order to reduce or damp a vibration and a shock which are generated in the corresponding gear shift range if it is determined that the corresponding gear shift range is the anti-judder-approval gear shift range.
German Patent Publication No. DE 10 2012 224 294 A1 discloses a method for anti-judder control of a vehicle which uses the power of a motor, wherein the method comprises the following: outputting an actual rotational speed of the motor via a controller; outputting a model rotational speed of the motor via the controller; outputting a vibration component on the basis of a difference between the output model rotational speed and the actual rotational speed of the motor via the controller; high-pass filtering of the vibration component via the controller in order to remove a fault component in the vibration component; delaying a phase of the filtered vibration component for a preset time via the controller in order to compensate the phase error occurring during the high-pass filtering; and applying the preset amplification to the filtered vibration component via the controller, during which amplification the phase is delayed for the preset time in order to generate an anti judder compensation torque.
U.S. Patent Publication No. US 2011 112 709 A1 discloses an anti-judder controller for a hybrid vehicle which comprises calculating a model speed of the motor, in a state in which a vibration of the drive train is not present, and calculating a difference between the model speed and a current speed.
The solution according to the invention for suppressing the mechanical oscillation of the drive train is intended to reduce or prevent the oscillation of the drive train without having to engage in the mechanical structure of the drive train. As a context, the acceleration of the vehicle is not to be markedly worsened either, and the subjective driving sensation, in particular the response behaviour to the accelerator pedal, is to be adversely influenced as little as possible for the driver.